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Radiant Barrier - money for nothing???


equinox's Avatar
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TX

08-08-11, 12:01 PM   #1  
Radiant Barrier - money for nothing???

My house is 7 years old and well insulated with 16 inches of blown cellulose. Just wondering what percent of additional energy reduction is typically achieved through the installation of radiant barriers. Texas of course has very hot summers and this year that is an understatement with a month already over 104F each day, but when looking at the installation costs of either paying someone to install on the high hip roof rafters that I am not able to do myself, or even doing it as a DIY by possibly just blanketing on top of the attic insulation what is a typical payback time period if there even is one? One local guy suggested a cost of around $4000 for the rafter installation, basically $1.00 per square foot of living space but my AC electric bills typically can run $500 in the hot season so something like a 10% energy reduction would never provide a reasonable payback period. Does anyone have any real life experience with these reflective products. I would not probably consider the spray on paint type as well. All the new construction in my area is using the radiant covered roof sheathing however.

 
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08-08-11, 02:06 PM   #2  
The radiant covered roof sheathing would be the best as it holds the heat at the roof level. From there it radiates back into the air or is swept away by convection or wind.

Once the energy is inside the attic, a RB simply isolates the heat to the roof side of the barrier, but that still requires some form of ventilation to get rid of it. Left between the bottom of the rafters or in the attic between the top of the insulation and the roof, you will still face convective air movement that will pass some of that energy into your home.

A RB will help, a little, but with $500 a month bills I would be looking for the smoking gun elsewhere. I know you said well insulated and I know 104° is hot, and it sounds like your home is in the 4000 sq ft range, but something is leaking.

A good energy audit is about $400 bucks and would quickly tell you where the weak spots are. There are DIY audit sites where you can start the process, but an auditor will run a blower door test and a duct test for leakage.

Where are your ac ducts and your air handler? In the attic? Sealing and insulating them could make a difference. If they are in the attic they are insulated, but r-6 vs that 16 inches of cellulose means they are naked. Between air leaks and the moving air you could be losing a lot right there.

Bud

 
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08-08-11, 04:11 PM   #3  
Perhaps your attic needs better ventilation.

 
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08-08-11, 06:40 PM   #4  
Radent barrier is good for the first couple of months. Once it gets a very light coating of dust it just heats up instead of reflecting. Like said the foil coated sheathing is best. The RB paint will be better in the long run because it's not affected by dust.

 
equinox's Avatar
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08-09-11, 08:27 AM   #5  
Thanks guys. Yes the HVAC's are in the attic (2 of them), and all the duct work is suspended flexible pipe. These are the ones that are plastic pipes I believe wrapped in an insulation foil wrap. I was wondering about how well they are sealed also, but never thought about the insulation around them, other than some rooms do not seem to cool as well as others. Thanks for that Bud. Is there a proper material and method used for upgrading the insulation value of them. I can foil tape where more is required due to leaking but can also add some more R value at the same time I am walking around the 16 inches of cellulose trying to find the next joist to stand on. LOL. The roof venting could also be an issue though it met the minimum local code back in 2004 I guess. I know of one door accessible attic space (solid panel door with weather strip) I use as a storage area that is completely sealed from the outside with no vent for instance and that space heats up where you have about 3 minutes to get in and out. Perhaps the code doesn't require that added vent specifically, and only is based on total roof area. Hey, it's Texas. I also have never confirmed airflow from the soffits, though I think some form of cardboard baffles were used by the builder. The soffits are hole perforated hardi board or similar. It's one of those houses with alot of roof structure, 2x12 trusses framed on site, and with a multiple roof line profile. Very typical of what you find in Northern Texas and where attic space becomes the Texas basement where it provides some storage and HVAC location. I am now convinced from Bud's comments that my first step should be to have a proper energy audit performed and maybe even a look through a thermo imaging camera to see what it shows. These houses are typically thrown up and occupancy ready in about 3 months and most of the site team are from south of the border who work hard as laborers but most have no trade skill, and can work all day even when it is 100F outside, so I also wonder if even some wall insulation was missed by them and the inspector who at that time during the building boom would have his day pretty much overloaded. I have seen these teams have a new house framed and pretty much closed up including windows in less than a work week. My concern around having the spray-on RB applied is in regard to ensuring that a proper material buildup be applied by whoever did it and that the product would not be thinned out to increase coverage. Both not easy to ensure, especially in a relatively new business concept where all kinds of people are already on board for the fast buck. I forgot to mention that the $500 buys me 80F inside as my attempt to keep costs manageable so it is not like I am trying to create the arctic in the desert heat.

 
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08-09-11, 09:01 AM   #6  
Check references on the energy auditor you select, they should be excited about the results they received. Read over one of their reports if you can. HERS rated or BPI certified.

One of the aspects of duct insulation is the moving air. If memory serves me, it is 400 cfm per ton of ac capacity. That's a wind chill factor on steroids. That will be interesting to look at in infrared while running. Leaks will glow and the ducts should be cold. He will need to adjust his camera for the emissivity of the foil, tricky.

As for what to add, we don't see many up here, but just lots of whatever is used. I'm sure others on here are from the hot country.

As for the enclosed space with no venting, there is probably an option depending upon where it is located. Do you have gable vents or a ridge vent? An incense stick for smoke will show you if the air flow is moving (be careful around the cellulose). A common failure is to not open the ridge when they install the vent. Sounds stupid, but all too often occurs. Your effective vent area should be in the range of 1 sq ft of vent for every 300 sq ft of attic floor and that's effective area. Most vent materials will have a derating for the air trying to squeeze through a bunch of small holes. A rough guess would be 50%.

Check what you have for venting and let us know. Also, pick up a remote temperature sensor to monitor what is going on up there. How high it goes and when.

Bud

 
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08-09-11, 02:11 PM   #7  
I live in N. Texas and did the rb foil AtticFoil® Do-It-Yourself Radiant Barrier Foil Insulation and it paid for itself the first summer.
I installed myself and the attic only gets to ~115-120 degrees. I have a 3400 sq. ft. and our bill has not been over $300 ($230 in july and projected to be $280 in Aug). Definitely staple foil to rafters, best way to keep heat out-which also keeps heat off ductwork and ac units. I also installed solar screens on any window w/alot of sun exposure, mainly S, E, and W side of the house since it faces North. We have louvered wooden blinds on most all of our downstairs windows anyway, which kept sunlight out quite well. Not quite sure why the dust would make such a difference, but evidently mine hasn't got dusty since I installed it. I do need to add a 20' run of ridge venting, but my house has hardiboard with drilled holes in soffits around entire house. You definitely need plenty of soffits for adequate ventilation. Good Luck!

 
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08-10-11, 04:13 AM   #8  
Thanks as this is good input and something else for me to consider. How long did it take you to install the RB? How did you deal with your insulation and ladder stapling scenario, assuming that you also may have a high hip roof, and tall rafters, and also in rough numbers what did the entire project end up costing? What I think you are telling me is that as a DIY project the RB solution does make some sense especially if you are seeing a payback after year 1. What kind of monthly bills were you seeing prior to the RB upgrade just for comparison? You have caught my interest now.

 
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08-31-11, 01:54 PM   #9  
Sorry I haven't got back to you, but I'm sure you won't be doing this until Dec/Jan. It took me 3 or 4 days, basically 2 weekends to complete as much as I could access.
Make sure you get an electric stapler, makes job much easier on your hands since some low spots are very tight. For the low/tight areas, I had a piece 3/4" plywood that I lied down on floor. It smushed the blown fg, but I fluffed it back up w/a little plastic yard rake when done in an area. I had to use an 8' ladder on the attic floor to get to apex area that is about 12-13' at highest point.
I cut 15 to 20' pieces of the foil downstairs on floor, folded them enough to handle and take upstairs and into attic. Started at one end and stapled it straight, then went on down stapling horizontally on rafters. Where you have an inverted V area, just cut the top of the barrier to allow heat to escape (refer to website on post--it has good info on installing). Cut out holes in foil for any existing vents. Work your way up and overlap an inch or 2 as you go, leaving a 3-4 inch gap at top of horizontal ridge line. Then make sure you add ridge vent if not already there. Payback was less than 1 summer down here. I go up into the attic now at 6:00pm and my temp gauge reads 120* F. We run AC for about 1 hr. in the morning when we're getting ready for work, and then it cuts on at ~4:00pm since we get home about 5. So it don't run all day long, like our friends do and complain about a $500-800 elect. bill!! Programmable thermostats are a must. We're saving $100+ a month from Apr. thru Oct. So far this summer our highest bill was $275. I paid less than $400 for 3 rolls of rb and stapler and in 3summers it's saved us prolly $2500. Definitely a DIY must, so don't pay nobody to screw you out of $4k when you can do it yourself.

 
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08-31-11, 08:15 PM   #10  
Thank you for that information igneous. You are right about waiting until things cool down, but for the small amount of material costs, this really does seem to make sense in doing it. I also may have an energy audit done as well to see if there are any other opportunities that could give me some good payback savings.

 
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09-02-11, 10:55 AM   #11  
Hell yeah, it's a no brainer. If the hot air don't get into the space to begin with, you don't have to worry about removing as much. That's all AC systems do, is remove heat. Yes, I had an audit done on my old house but not on the new one. Think alot depends on how old house is. I just make sure all door/windows are sealed good during winter and no cold air is intruding. Get double paned windows installed if you don't have them. One thing I also did for my door into garage and external doors (3) was install the spring loaded hinges on bottom and top to close door quickly. They work great and you can get them at Home depot, etc.

 
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